The present invention relates to compounds of the formula (1) and to the use thereof in electronic devices, and to electronic devices which comprise these compounds.
The general structure of organic electroluminescent devices is described, for example, in U.S. Pat. Nos. 4,539,507, 5,151,629, EP 0676461 and WO 98/27136. However, there is still a need for improvement in these devices:    1. The efficiency should still be improved, especially in the case of fluorescent OLEDs.    2. The operating lifetime is still short, in particular in the case of blue emission, and consequently there is still a need for improvement here.    3. The operating voltage is quite high, especially in the case of fluorescent OLEDs, and should therefore be reduced further in order to improve the power efficiency. This is of major importance, in particular, for mobile applications. Further improvements are desirable here, in particular in the case of charge-transport materials.    4. In the case of hole-transport materials in accordance with the prior art, the voltage is dependent on the layer thickness of the hole-transport layer. In practice, a greater layer thickness of the hole-transport layer would frequently be desirable. However, this cannot be achieved using materials in accordance with the prior art owing to the associated increase in voltage.    5. Many materials which are used in accordance with the prior art in organic electroluminescent devices tend to crystallise on the vapour-deposition source in the process for the production of the electroluminescent device and thus clog the vapour-deposition source. These materials can therefore only be employed in mass production with increased technical complexity.
Arylamines are used as hole-transport and -injection materials. Materials of this type based on indenofluorenes are disclosed, for example, in WO 06/100896 and WO 06/122630. The indenofluorenamines described above have disadvantages in processability: during the vapour-deposition or coating process, premature deposition and thus a complication of the industrial process may occur. In addition, hole-transporting materials generally frequently have low electron stability, which results in short lifetimes of the associated diodes in operation. There continues to be a need for improvement here.
Furthermore, quinacridine derivatives and the use thereof in electronic devices are disclosed in WO 07/064,104.